17-03-2014, 06:07 PM
ABSTRACT
Weight perception in virtual environments generally can be
achieved with haptic devices. However, most of these are hard to integrate
in an immersive virtual environment (IVE) due to their technical
complexity and the restriction of a user’s movement within
the IVE. We describe two simple methods using only a wireless
light-weight finger-tracking device in combination with a physics
simulated hand model to create a feeling of heaviness of virtual
objects when interacting with them in an IVE. The first method
maps the varying distance between tracked fingers and the thumb to
the grasping force required for lifting a virtual object with a given
weight. The second method maps the detected intensity of finger
pinch during grasping gestures to the lifting force. In an experiment
described in this paper we investigated the potential of the
proposed methods for the discrimination of heaviness of virtual objects
by finding the just noticeable difference (JND) to calculate the
Weber fraction. Furthermore, the workload that users experienced
using these methods was measured to gain more insight into their
usefulness as interaction technique.
At a hit ratio of 0.75, the determinedWeber fraction using the finger
distance based method was 16.25% and using the pinch based
method was 15.48%, which corresponds to values found in related
work. There was no significant effect of method on the difference
threshold measured and the workload experienced, however
the user preference was higher for the pinch based method. The
results demonstrate the capability of the proposed methods for the
perception of heaviness in IVEs and therefore represent a simple
alternative to haptics based methods.
Index Terms: B.4.2 [Input/Output Devices]: Channels and
controllers; H.3.4 [Systems and Software]: Performance evaluation;
H.5.2 [User Interfaces]: Interaction styles; I.3.7 [Three-
Dimensional Graphics and Realism]: Virtual Reality
1 INTRODUCTION
Interaction and manipulation of objects is a fundamental task not
only in the real world but also in virtual environments (VEs). In
the real world, human beings perceive objects encountered in daily
life by using their sense organs and transmitting the stimulus information
to their brain. For instance, touch can provide information
about size or texture. Analogously, one of the key characteristics
in virtual reality is the real-time multi-modal sensory interaction
between the human operator and the virtual world. In order to perceive
the virtual world and objects in it, VEs not only involve vision
but also other sensory modalities, such as the haptic sense in particular.
The work presented in this paper concentrates on simulating the
weight of virtual objects. Various psychophysical studies have been
conducted to understand the phenomenon behind the perception
of weight. Many factors play a role in the perception of heaviness,
including surface texture, size, materials, touch and muscle
sense [13, 5, 8, 7]. In terms of size, for instance, according to Carpentier’s
size-weight illusion study, when two equally heavy objects
of different sizes are lifted, the smaller object is perceived as being
heavier, which was shown to be valid in VR [15]. Weber’s finding
suggests that weight discrimination is improved by voluntary muscle
force, after which many studies focused on and concur the role
of touch and muscle force on perceived weight.
Weight perception is the combination of two main force sensations.
One is the tactile force sensation, which is the outer information
perceived by the cutaneous mechanoreceptors while grasping
the objects. These include the skin pressure and grip force. The
other is the proprioceptive force sensation that is perceived by the
muscle spindles or tendon organs, and is the internal information
involving muscle force or joint position. A number of devices have
been proposed that simulate the reaction force or vertical stress at
the fingers, the shearing stress, or vibration of selected tactile receptor,
or reproduce the proprioceptive sensations to provide weight
sensations [21, 10, 12, 17, 16, 22, 23]. However, many of these devices
suffer through drawbacks, such as being expensive, large and
complex, being grounded to a surface, or being heavy and uncomfortable.
Additionally, many of these are desktop based and cannot
easily be integrated into immersive virtual environments (IVE), as
they would restrict the user’s working area to that of the device or
would obstruct the user’s view, and thus reducing the feeling of
presence.
Weight perception in virtual environments generally can be
achieved with haptic devices. However, most of these are hard to integrate
in an immersive virtual environment (IVE) due to their technical
complexity and the restriction of a user’s movement within
the IVE. We describe two simple methods using only a wireless
light-weight finger-tracking device in combination with a physics
simulated hand model to create a feeling of heaviness of virtual
objects when interacting with them in an IVE. The first method
maps the varying distance between tracked fingers and the thumb to
the grasping force required for lifting a virtual object with a given
weight. The second method maps the detected intensity of finger
pinch during grasping gestures to the lifting force. In an experiment
described in this paper we investigated the potential of the
proposed methods for the discrimination of heaviness of virtual objects
by finding the just noticeable difference (JND) to calculate the
Weber fraction. Furthermore, the workload that users experienced
using these methods was measured to gain more insight into their
usefulness as interaction technique.
At a hit ratio of 0.75, the determinedWeber fraction using the finger
distance based method was 16.25% and using the pinch based
method was 15.48%, which corresponds to values found in related
work. There was no significant effect of method on the difference
threshold measured and the workload experienced, however
the user preference was higher for the pinch based method. The
results demonstrate the capability of the proposed methods for the
perception of heaviness in IVEs and therefore represent a simple
alternative to haptics based methods.
Index Terms: B.4.2 [Input/Output Devices]: Channels and
controllers; H.3.4 [Systems and Software]: Performance evaluation;
H.5.2 [User Interfaces]: Interaction styles; I.3.7 [Three-
Dimensional Graphics and Realism]: Virtual Reality
1 INTRODUCTION
Interaction and manipulation of objects is a fundamental task not
only in the real world but also in virtual environments (VEs). In
the real world, human beings perceive objects encountered in daily
life by using their sense organs and transmitting the stimulus information
to their brain. For instance, touch can provide information
about size or texture. Analogously, one of the key characteristics
in virtual reality is the real-time multi-modal sensory interaction
between the human operator and the virtual world. In order to perceive
the virtual world and objects in it, VEs not only involve vision
but also other sensory modalities, such as the haptic sense in particular.
The work presented in this paper concentrates on simulating the
weight of virtual objects. Various psychophysical studies have been
conducted to understand the phenomenon behind the perception
of weight. Many factors play a role in the perception of heaviness,
including surface texture, size, materials, touch and muscle
sense [13, 5, 8, 7]. In terms of size, for instance, according to Carpentier’s
size-weight illusion study, when two equally heavy objects
of different sizes are lifted, the smaller object is perceived as being
heavier, which was shown to be valid in VR [15]. Weber’s finding
suggests that weight discrimination is improved by voluntary muscle
force, after which many studies focused on and concur the role
of touch and muscle force on perceived weight.
Weight perception is the combination of two main force sensations.
One is the tactile force sensation, which is the outer information
perceived by the cutaneous mechanoreceptors while grasping
the objects. These include the skin pressure and grip force. The
other is the proprioceptive force sensation that is perceived by the
muscle spindles or tendon organs, and is the internal information
involving muscle force or joint position. A number of devices have
been proposed that simulate the reaction force or vertical stress at
the fingers, the shearing stress, or vibration of selected tactile receptor,
or reproduce the proprioceptive sensations to provide weight
sensations [21, 10, 12, 17, 16, 22, 23]. However, many of these devices
suffer through drawbacks, such as being expensive, large and
complex, being grounded to a surface, or being heavy and uncomfortable.
Additionally, many of these are desktop based and cannot
easily be integrated into immersive virtual environments (IVE), as
they would restrict the user’s working area to that of the device or
would obstruct the user’s view, and thus reducing the feeling of
presence.